A 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system includes two working modes: frequency division duplexing (Frequency Division Duplexing, FDD for short) and time division duplexing (Time Division Duplexing, TDD for short). In the 3GPP LTE system, to support hybrid automatic repeat, a terminal needs to feed back a hybrid automatic repeat request-acknowledgement (Hybrid Automatic Repeat request-Acknowledgement, HARQ-ACK for short) to a base station by using a physical uplink control channel (Physical Uplink Control Channel, PUCCH for short) and a physical uplink shared channel (Physical Uplink Shared Channel, PUSCH for short). When the terminal feeds back an acknowledgement (Acknowledgement, ACK for short) to the base station, it indicates that the terminal correctly receives a message. When the terminal feeds back a negative acknowledgement (Negative Acknowledgement, NACK for short) to the base station, it indicates incorrect receiving at the terminal, and the base station needs to perform retransmission.
In 3GPP LTE Rel 10/11, to satisfy a requirement of the International Telecommunication Union for the peak data rate of the 4th generation communications technology, carrier aggregation (Carrier Aggregation, CA for short) is introduced. Aggregated carriers are referred to as component carriers (Component Carrier, CC for short), and are also referred to as a serving cell. In the carrier aggregation technology, two or more component carriers are aggregated to provide higher bandwidth. In the LTE Rel-8/9, user equipment (UE) can access only one component carrier to perform data transceiving; while in the LTE-A, UE may access, according to capabilities of the UE and service requirements, multiple component carriers to perform data transceiving. In an existing carrier aggregation system, generally, carriers deployed on a same base station (Evolved NodeB, eNB for short) are aggregated, or carriers under a macro cell and a micro cell that have an ideal backhaul link (Backhaul) are aggregated. In an existing CA system, hybrid automatic repeat request-acknowledgement information is sent only on a primary carrier, and duplexing modes of aggregated component carriers are the same, and are FDD or TDD.
In a subsequent LTE system, carrier aggregation may evolve to support aggregation of different duplexing modes, that is, duplexing modes of aggregated component carriers may be different, for example, duplexing modes of some component carriers are FDD and duplexing modes of other component carriers are TDD. In an existing CA system, the HARQ-ACK is sent only on a primary carrier, and for aggregation of different duplexing modes, the primary carrier may be an FDD carrier or a TDD carrier. In this evolution direction, if the primary carrier is a TDD carrier and another component carrier is an FDD carrier, an HARQ-ACK corresponding to the FDD carrier also needs to be fed back on the TDD carrier. In an existing system, for the FDD carrier, HARQ-ACK timing of the FDD carrier is n+4, that is, an HARQ-ACK corresponding to a PDSCH transmitted in a downlink subframe n is fed back in an uplink subframe n+4. However, if an HARQ-ACK corresponding to an FDD carrier is fed back on a TDD carrier, because only some subframes of a radio frame on the TDD carrier are used for uplink transmission, if HARQ-ACK timing of existing FDD is used, for downlink subframes on some FDD carriers, there is no corresponding uplink subframe used to feed back an HARQ-ACK. If these downlink subframes are not scheduled, resources may be wasted. Therefore, how to transmit an HARQ-ACK during aggregation of carriers of different duplexing modes needs to be resolved.